The goal of this research is to increase the clinical utility of the CEA assay for diagnosis and monitoring of malignant disease, particularly cancer of the large bowel. The approach being used is to define CEA chemically and to identify distinctive portions of the molecule against which antisera can be prepared. A clinical study comparing the utility of CEA and TEX for the diagnosis and monitoring of various forms of cancer has been initiated. The finding that the carbohydrate groups may be removed from CEA by treatment with anhydrous hydrofluoric acid has provided us with a more homogeneous preparation for cleavage to peptide fragments, which are now being sequenced.